1. Field of the Invention
The present invention relates to an inkjet recording apparatus for executing recording using a recording head for ejecting inks and to a recovery control method of recovering the ejecting state of the recording head.
2. Related Background Art
Recording apparatuses such as a printer, copy machine, facsimile, and the like are arranged to record an image composed of a dot pattern on a recording member such as a paper sheet, plastic thin sheet, and the like. Recording systems employed by the recording apparatuses can be classified into an inkjet system, wire dot system, thermal system, laser beam system, and the like.
Among them, the inkjet system ejects flying ink droplets as a recording liquid from ejection ports acting as openings located at the extreme ends of the nozzles of a recording head (inkjet recording head) and executes recording by depositing the ink droplets on a recording member.
In the recording apparatuses employing the inkjet system, it is conventionally known that the ejection ports of the recording head become clogged because the inks ejected from the ejection ports are evaporated, and thus a recorded state is deteriorated or it becomes difficult to execute recording in some cases. To suppress the evaporation of the inks, there is generally provided a mechanism for capping the ejection ports of the recording head using a capping member when the recording apparatus is not in operation. In the above arrangement, it is known to switch the recording apparatus between a closed state and an open state according to whether the recording apparatus is in a recording state or in a waiting state by a mechanism for relatively moving the capping member and the recording head so that the ejection ports are shut off from the outside air by capping the ejection ports with the capping member by causing the capping member to come into intimate contact with the surface on which the ejection ports of the recording head are formed (referred to as the “cap closed state” or the “closed state”) and that the capping member is separated from the surface on which the ejection ports are formed (referred to as the “cap open state” or the “open state”).
While the evaporation of inks is suppressed by the above mechanism of the cap, bubbles are gradually generated in the ink nozzles as a period elapses, whereby printing defects may be caused by the bubbles. Further, the viscosity of the inks in the ink nozzles increases as the period elapses, whereby the printing defects may be caused. The phenomenon that the bubbles are generated in the nozzles as the period elapses is caused by the fact that a gas dissolved in the inks as a liquid appears as the bubbles. Further, deterioration of a printed state due to the printing defect is caused by the fact that inks are unstably ejected or are not ejected owing to the increase of the viscosity of the inks existing in the ejection ports of the nozzles and the fact that the color materials of the inks and the impurities in the inks precipitate around the ejection ports as a solvent in the inks evaporates. To cope with the deterioration of the printed state described above, many inkjet recording apparatuses employ a method of executing a print operation by recovering the recording head by forcibly sucking the inks from the outside.
In the recovery operation executed by sucking the inks, a large amount of the inks is discharged by executing the operation once. Thus, it is preferable to execute the recovery operation as less frequently as possible to reduce a consumed ink amount. This is because a running cost can be particularly suppressed as well as the capacity of a waste inks accommodation unit for accommodating discharged inks can be reduced by suppressing the amount of the inks discharged by the recovery operation. For this purpose, it is known in conventional recording apparatuses to provide a timer or an arrangement for measuring a period similar to the timer with the recording apparatus, to measure a period elapsed from a last-executed suction operation, and to determine whether or not inks are to be sucked according to the elapsed period.
As an example, when the suction operation is not executed even if, for example, two or five days have elapsed, a suction recovery operation (referred to as “timer suction”) is executed in an amount of suction set according to an elapsed period. Further, when the elapsed period is shorter than two days, a timer preliminary ejection operation, which is a recovery operation executed by ejecting inks, is executed according to the elapsed period. With the above operations, the increase in viscosity of the inks in the nozzles and the precipitation of the color material and the impurities of the inks around the nozzles can be prevented.
In the arrangement of the conventional recording apparatuses, since the period elapsed from the last-executed suction operation is measured based on the timing at which the suction operation is executed, there is not considered a case in which a degree of evaporation of inks differs depending on a state of the recording apparatus. Thus, there is case in which the ejecting state of the recording head cannot be favorably recovered. Further, when preference is given to the recovery of the ejecting state of the recording head, it is contemplated to previously set to execute a suction recovery operation even if an elapsed period is relatively short, assuming that the ink has evaporated in a considerable amount. In this case, however, there is a possibility that the suction recovery operation is executed even if the operation is not necessary judging from the degree of evaporation of the inks.
Further, since it is preferable to suck the inks as less frequently as possible to suppress the consumed ink amount, the suction recovery operation is executed only when the elapsed period has reached a certain degree of a long period. In this case, however, the recording head may not be sufficiently recovered depending on a state of the recording apparatus.
For example, when only black characters are continuously printed (for example, two or three hours) and then a color image is recorded, the nozzles for ejecting color inks are continuously kept in the cap open state without executing recording. In this case, the color materials and the impurities of the color inks precipitate around the color ink nozzles and may be crystallized depending on evaporating conditions. Accordingly, printing defects may be caused by these precipitants and the crystallization of the color materials and impurities.
Likewise, a special sheet such as a glossy medium is generally controlled such that it is not printed with a black pigment. When, however, an image is recorded on the special sheet by color printing (for example, continuously for two to three hours) and then characters are printed using the black pigment, the nozzles for ejecting the ink containing the black pigment are continuously kept in the cap open state without executing recording. As a result, the nozzles are clogged by the adhesion of the inks whose viscosity is increased because the inks are dried, thereby printing defects occur.
Accordingly, in an arrangement in which the timer preliminary ejection described above is executed when a period, during which the suction is not executed, is short, the recovery operation cannot be executed sufficiently in the case of the example described above, thereby the printing defect is caused.
As described above, the cap of the nozzles for ejecting a certain ink may be continuously kept in the open state depending on a recording operation. Inks are evaporated and dried and precipitants are produced in an elapsed period in different degrees, depending on whether the cap is opened or closed. Accordingly, the conventional arrangement for determining the execution of the suction recovery operation based on the elapsed period has a problem in that inks are wastefully consumed in the suction recovery operation and that defective ejection occurs more frequently.